The crowd walking could all collapse the bridge

In addition to poor design, poor construction quality, the impact of natural disasters, . the researchers also found another factor that could cause a bridge collapse: the crowd walked steadily.

In April 1983, a brigade of soldiers marched through the English Broughton suspension bridge. According to records at the time, the bridge was broken at the feet of soldiers, throwing dozens of people into the water.

After this happened, the British army issued new regulations: soldiers passing a long bridge could not walk evenly or march smoothly, in order to prevent recurrence.

Pedestrians are advised not to walk all over the group to cross the bridge to prevent the risk of causing the bridge to collapse.(Artwork: Word Press)

Structures like bridges and buildings, although they look solid and unmodified, possess a natural frequency of vibrations within them. A force that impacts an object with a frequency equal to the natural vibration frequency of the object, will amplify the vibration of the object - a phenomenon known as "mechanical resonance".

Sometimes, your car vibrates violently when you press the accelerator to a certain speed, and a girl sitting on a swing can move to a higher position with just a little strength by swinging. his legs. According to experts, the principle of mechanical resonance leading to these phenomena is also "worked out" when the crowd of pedestrians walks steadily through a bridge.

If the soldiers marched in unison across the bridge, they created a force at the frequency of the walk. If their step frequency is close to the natural vibration frequency of the bridge and the mechanical resonance is large enough, the bridge can vibrate until it collapses because of that movement.

A recent incident that reminded this phenomenon was in June 2000, when the Millennium Bridge in London was held in a loud and noisy way. A crowd gathered on the bridge, and their footsteps made the bridge shake slightly."Many random walkers have steps that correspond to the vibrations (naturally) of the bridge, so they accidentally amplified them," quoted a scientific report published in 2005 in the journal Nature.

Although engineers emphasized that the Millennium Bridge was never at risk of collapse, the authorities had "closed" the bridge for about a year for the construction teams to install shock absorbers and anti-shock devices. vibrate to minimize vibration caused by pedestrians.